A communication system can be seen as a facility that enables communications between two or more entities such as user equipment and/or other network elements, also called nodes, associated with the communication system. A communication system typically operates in accordance with a given standard or specification which sets out what the various entities associated with the communication system are permitted to do and how that should be achieved.
Examples of communication systems may include fixed communication systems, such as a public switched telephone network (PSTN), wireless communication systems, such as a public land mobile network (PLMN), and/or other communication networks such as an Internet protocol (IP) transport network and/or other packet switched data networks. Various communication systems may simultaneously be concerned in a connection.
Wireless communication systems include various cellular or otherwise mobile communication systems using radio frequencies for sending voice or data between stations, such as user equipment (UE) (e.g. mobile stations, MS) and base transceiver stations (BTS), also called base stations. Examples of mobile communication systems are the global system for mobile communications (GSM), general packet radio service (GPRS) and the so-called third generation (3G) mobile communication systems, such as the universal mobile telecommunications system (UMTS) terrestrial radio access network (UTRAN).
An example of the IP transport network is the Internet, which is a global network formed by the interconnection of numerous smaller networks all adapted to use the Internet protocols, such as the Internet Protocol (IP) and the Transmission Control Protocol (TCP), and a common address structure. In addition to said protocols, the IP transport network may include a number of auxiliary protocols, such as the address resolution protocol (ARP), open shortest path first (OSPF) and Internet control message protocol (ICMP). The IP transport network provides transfer of data in links provided between nodes, i.e. hosts and routers, within and between the smaller networks.
The IP network operates according to a principle of layered communication, where lower layers serve upper layers and adjacent layers communicate over an interface. An example of a layered communication model is the Open System Interface (OSI) reference model. The layers of the OSI reference model may be called the physical layer (the first layer), the data link layer (the second layer), the network layer (the third layer), the transport layer (the fourth layer) and the application layer (the fifth layer).
The data link layer (i.e. the second layer, L2) controls data flow, handles transmission errors, provides physical addressing and manages access to the physical medium. In the data link layer, data link layer devices, such as bridges and switches, take care of these functions. The data link layer may use Ethernet protocol, for example.
The network layer takes care of routing, i.e. determining optimal routing paths and transferring the data packets over the IP network from an originating party, i.e. source host, to a terminating party, i.e. destination host. In determining optimal routing paths, the network layer may use routing algorithms and routing tables. A routing path typically goes through routers. The network layer transfers information using so-called protocol address of the terminating party in determining the physical addresses of the routers along the routing path. In the network layer, the IP version 4 protocol (IPv4) or the IP version 6 protocol (IPv6) may be used. Other protocols may also be used. Examples of such protocols may include the IPX, NetBIOS, DECnet, SNA, AppleTalk and so on.
In an IP network each node, including hosts and routers, has an address, which is unique for the element. The Internet Engineering Task Force (IETF) has developed an addressing architecture of the IP for assigning identifiers for node interfaces. A single interface of a node has at least one IP address, but may have multiple IP addresses as well.
Both the IPv4 and the IPv6 provide a structure for defining the IP addresses. The IPv4 defines addresses of 32 bits and the IPv6 increases the address size to 128 bits. The IP address consists of two parts: the network portion and the host portion. The network portion identifies the network to which the node is connected and may also be called a subnet prefix. The host portion identifies the host in the network, or in other words, the interface on which the host is attached to the link. In the IPv6, the host portion is called as an interface identifier (interface ID).
In the IPv4, the number of addresses is limited and a careful address planning is needed. Gateways (i.e. IP Routers) are typically used to create addressing structure where a private network has an independent private address space (intranet) and only a limited amount of public addresses. The DHCP (Dynamic Host Configuration Protocol) is applied usually for autoconfiguring IP addresses and other network settings to the IPv4 hosts.
In the IPv6, there are much more available IP addresses than in the IPv4. An IPv6 address consists of 64-bit long prefix portion and 64-bit long interface ID portion. The IPv6 incorporates also site-locally and link-locally scoped addresses in addition to the globally routable addresses. Site-locally scoped addresses are used for communications inside private networks as these addresses shall not route outside the defined boundary. Link-locally scoped addresses are used for communications between nodes that are connected to the same link i.e. a medium over which nodes can communicate at the link layer. Example of such a link is a simple or bridged Ethernet. An IPv6 node may assign to its interface IPv6 addresses with multiple scopes depending on its communication needs with other nodes that may reside in the same link, site, or in some other public IPv6 network. The scoped IPv6 addresses are formed so that the same interface ID portion is joined with different prefix portions that are defined for each scope.
In the IPv6, an address autoconfiguration process is provided for multicast-capable links. In the autoconfiguration, a node, i.e. a host or a router, generates a preliminary, also called tentative, link-local address by appending the interface ID to a known link-local prefix. An address is tentative until its uniqueness is verified. The node verifies the uniqueness of the tentative link-local address by making enquiries in the neighboring nodes. If the verification shows that the tentative address is unique, said address is assigned to the interface. If the verification shows that the address is already used by another node, there may be an alternative interface ID to be tried or a manual configuration may be required. A host may then receive further information from a router and may continue its autoconfiguration based on this information.
The mobile communication networks as defined by the third generation partnership project (3GPP) are expected to apply IP transport option in radio access networks (RAN), for example in the UTRAN. FIG. 1 shows an exemplifying architecture for the IP transport network 1, i.e. IP network of routers, as defined by the 3GPP. A router 16, 18, 44 connecting a host, such as a transceiver network element, e.g. a Node B 12, 14, or a controller network element, e.g. radio network controller (RNC) 42, to the IP network 1 may be called an Edge Router. Typically, each Node B and RNC 12, 14, 42 needs its own router 16, 18, 44 to connect the Node B 12, 14 and the RNC 42 with the IP network 1. In some cases, two or more network elements, such as two or more transceiver network elements, such as two or more Node Bs 22, 24, or a transceiver network element, such as a Node B 32, and a controller network element, such as a RNC 34, may be directly connected to each other with a point-to-point link. This connection takes no benefit from the IP infrastructure and no intermediate router is needed between the two transceiver network elements 22, 24 or 32, 34. Each network element remains an individual IP node.
It shall be appreciated that FIG. 1 is only an example of a simplified IP transport network. The number, type and order of the entities may differ substantially from the shown. It shall also be appreciated that the terms used in the context of FIG. 1 refer to the 3G mobile communication system as defined by the 3GPP. In the second generation (2G) mobile communication systems, such as the GSM, the transceiver network element is typically called a base transceiver station (BTS) or simply base station and a controller network element is typically called a base station controller (BSC).
When IP transport is applied in the radio access network, it is obvious that the base stations become IP nodes that may build up an internal local area network (LAN), based for example on the Ethernet protocol. This is shown in FIG. 2, where a base station node 200 is build of multiple base station modules each comprising an IP host connected to the internal LAN 210 of the base station node. The base station node 200 may be a telecommunication equipment comprising a cabinet housing multiple base station hardware modules 204, 205, 206, 207 that together implement for example the Node B functionality according to the 3GPP specifications. The base station modules may typically be replaceable plug-in units. The base station node may sometimes be also called a base station cabinet as often a logical base station fits into a single physical equipment, i.e. the cabinet.
The FIG. 2 arrangement is similar to the ensemble of Node Bs 12, 14 and Edge Routers 16, 18 of FIG. 1 corresponding to the base station nodes 200, 250 and IP routers 203, 253 of FIG. 2, respectively. As shown in FIG. 2, the IP router 203 as a network layer forwarding device separates, or isolates the base station internal IP subnet and Ethernet LAN from other networks, such as the external IP transport network, all the traffic that happens just between the base station internal modules. Therefore, instead of using globally unique Ethernet addresses, the base station modules may assign dynamically (autoconfigure) locally scoped Ethernet addresses to be used for the base station internal communications at the link layer.
One physical transport module of the base station may include both the IP router and L2 switch functions. Alternatively, the IP router function may be implemented by a separate, base station external physical device, into which the base station is connected. In such a case, the transport module may contain only the L2 switch function.
One of the base station modules is a transport module 202 connected with an IP router 203 and connecting the base station internal LAN 210 to the external IP transport network 1 of the radio access network (e.g. UTRAN). The IP router 203 provides a default gateway function to the base station modules 204, 205, 206, 207 comprising IP hosts. The internal LAN 210 of the base station node 200 forms a single IP subnet configured in the IP router 203 and the base station modules 204, 205, 206, 207 share the same IP subnet prefix for communicating outside the internal LAN 210. As several base station modules may be included in each base station node, and each base station module may represent one or more IP hosts, a base station node as a network element may require easily tens of Ethernet and IP addresses.
If two or more base station nodes 200, 250 need to be connected to the IP transport network 1, each base station node 200, 250 needs an IP router 203, 253, as shown in FIG. 2. Each base station node 200, 250 thus forms its own internal LAN 210, 260 and has its own IP subnet prefix.
The amount of required IP subnets increase when all the base station nodes are interconnected using an IP routed network. In the FIG. 1 architecture, each Node B represents one IP subnet that has to be advertised using routing protocols to other routes in the IP network. The amount of required public IP addresses in each IP subnet depends on how many IP hosts in the base station nodes has to be able to communicate with IP hosts connected to the base station external IP networks. Thus, the amount of addresses towards the external IP network increases quickly.
Therefore, there is a need for alternative ways of configuration of IP addresses.